Finite Element Analysis of Endocrown and Post-and-Core Abutments for Removable Partial Dentures with Different Framework Materials.

PURPOSE: To evaluate the stress distribution in endocrowns and post-and-core crowns used as abutments for a Kennedy Class I removable partial denture constructed with different framework materials. MATERIALS AND METHODS: 3D models of a Kennedy Class I mandible were constructed. Cobalt-chromium (Co-Cr) and polyether ether ketone (PEEK) frameworks were simulated for Models 1 and 2, respectively. An endocrown and a fiber post-and-core crown for the mandibular left and right second premolar abutments, respectively, were simulated for both models. Lithium disilicate porcelain was defined for the crowns. A 200-N occlusal force was applied in the vertical and 30-degree oblique directions. RESULTS: The von Mises stresses were evaluated for the abutments and prostheses, and the principal stresses for the cortical bone under vertical and oblique loading. Endocrowns showed lower stress values than post-and-core crowns in both models. Post-and-core crowns generated the highest stress in Model 2 under vertical loading. The PEEK framework caused higher stress values on the abutments than Co-Cr. Compressive stresses were higher than tensile stresses in cortical bone. The highest compressive stress was observed around the left premolar cortical bone area in Model 1 under oblique loading. Oblique loading caused lower stress values than vertical loading, except for on the minor connectors and cortical bone. CONCLUSION: From a biomechanical perspective, endocrowns may be more advantageous than post-and-core crowns when used as abutments for a Kennedy Class I removable partial denture. In addition, Co-Cr frameworks showed more favorable stress distribution on abutments than PEEK frameworks. Int J Prosthodont 2023;36:203-215. doi: 10.11607/ijp.7269.

Effect of Different Light-Curing Modes on Bond Strength of Ceramic Laminate Veneers.

PURPOSE: To investigate whether high-level irradiance and short light exposure times with light-emitting diode (LED) curing units could provide bond strength comparable to halogen lights for ceramic laminate veneers (CLVs). MATERIALS AND METHODS: A total of 160 extracted human maxillary central incisors were prepared to receive CLVs (lithium disilicate) in shades A1 and A3.5. CLVs were luted with light-curing (LC) and dual-curing (DC) resin cements using four protocols: 3 seconds in extra power mode, 8 seconds in high power mode, or 10 seconds in standard mode with an LED unit, or 40 seconds with a conventional halogen light from all aspects (n = 10). Following thermal cycles, shear bond strength test was performed with a universal testing machine. Data were analyzed using one-way analysis of variance and post hoc Tukey test. Failure modes were classified under a stereomicroscope, and data were analyzed using Pearson chi-square test (P = .050). RESULTS: According to the intragroup comparison of different irradiation protocols, the mean shear bond strength of the A1-LC-10 group was found to be significantly higher than that of the A1-LChalogen group (P = .026). Shear bond strength values of the A1-LC-10 group and A3.5-LC-10 group were significantly higher than that of the A3.5-DC-10 group (P = .003). The A3.5-DC-3, A3.5-LC-3, and A1-DC-8 groups revealed the significantly most adhesive failures, and the A1-LC-8 group revealed the most mixed failures (P < .001). CONCLUSION: Both light and dark ceramic shades with LC cement combination responded the best to the standard mode of 10-second exposure time with LED application. However, with conventional halogen light application, the highest bond strength values were obtained with DC cement and light ceramic shade combination.

Three-Dimensional Finite Element Analysis of Different Implant Configurations in Enlarged First Molar Areas.

PURPOSE: The purpose of this in silico study was to determine appropriate implant treatment planning using three implant diameters and four different superstructures in enlarged mandibular first molar areas. MATERIALS AND METHODS: A mandibular bone block was constructed, and four configurations using three implants (2.9 × 10 mm, 4.1 × 10 mm, and 4.8 × 10 mm) were created for the first molar area. The four superstructures were designed as one large crown for a wide-diameter implant, a crown with a cantilever for a wide-diameter implant, two splinted crowns of one standard-diameter and one narrow-diameter implant, and two separate crowns of one standard-diameter and one narrow-diameter implant. Vertical loads of 200 N and oblique loads of 100 N were applied to various predetermined spots on the occlusal surfaces of these superstructures. Principal and von Mises stresses were analyzed on both the cortical bone and implant structures. RESULTS: Stresses were intensified in the cortical bone around the implant neck and implant-abutment interface. The highest compressive (36.97 MPa) and von Mises (265.71 MPa) stress values were noted in the model with standard-and narrow-diameter implants supporting two separate crowns. The lowest compressive (15.86 MPa) and von Mises (16.36 MPa) stress values were observed in the model with a distally positioned wide-diameter implant supporting the crown with a cantilever. CONCLUSION: In an enlarged first molar area, a configuration with a wide-diameter implant near the second molar and a cantilevered crown might distribute stresses more favorably than other configurations.

Advantages and limitations of implant surgery with CAD/CAM surgical guides: A literature review.

BACKGROUND: The purpose of this study is to review the available literature associated with implant surgery using computer-aided design/computer-aided manufacturing (CAD/CAM) surgical guides and discuss the advantages and disadvantages of this advanced technique. MATERIAL AND METHODS: An electronic literature search was conducted in the PubMed database for the relevant information on implant placement with CAD/CAM surgical guides. This review was constructed following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Articles were limited to those published within the past 10 years and in the English language. Only clinical studies were included. Inclusion criteria were: studies including 10 implants or more and studies presenting angular deviations in degrees and linear deviations in millimeter. Observational studies, reviews, animal studies, in vitro studies, case reports, simulation studies were excluded. Nine articles were included for qualitative synthesis. RESULTS: The initial search detected 61 articles, and after screening abstracts, a total of 15 articles were selected for full-text review. After the full-text analysis of the 15 articles, six articles were excluded as they did not meet inclusion criteria for study design, study population, and implant placement with data presentation for angular and linear deviations. Ultimately, nine articles providing angular and linear deviations between planned and actual placed implants were used in this review. Common problems that may be encountered by clinicians were listed, and recommendations were made on how to avoid those problems. CONCLUSIONS: It has been suggested that although unrealistic expectations are often associated with implant placement with CAD/CAM surgical guides, there is no impeccable accuracy in the clinic. This review demonstrated that the practitioners should be aware of the angular and linear deviations up to 5 ° and 2.3 mm. Therefore, inexperienced dentists should obtain adequate training and be familiar with the basic steps with CAD/CAM surgical guides to avoid complications. Key words:CAD/CAM, CBCT, implant, stereolithography, surgical guide.

Evaluation of Stress Distribution on Mandibular Implant-Supported Overdentures With Different Bone Heights and Attachment Types: A 3D Finite Element Analysis.

The biomechanical behavior of the edentulous mandible with bone irregularities that has been rehabilitated with implant-supported overdentures has become an important factor for treatment planning. Restorative options, including dental implants with various attachments, affect the stress distribution. The purpose of this study was to evaluate the stress distribution of cortical bone around the implant neck and implant structures in overdentures with two different attachment types at the edentulous mandible and with different bone heights using three-dimensional finite element analysis. Five three-dimensional models of an edentulous mandible were designed and implemented. Ten models were constructed with ball and locator attachments. Static bilateral and unilateral vertical and oblique occlusal loads with magnitudes of 100 N were applied to the overdentures. The principal stresses were higher in the presence of oblique loads compared to vertical loads in all the analyzed models. Maximum principal stresses were observed around the mesial side of the contralateral implant, and the minimum principal stresses were noted around the distal side of ipsilateral implant during unilateral vertical loading. These patterns were reversed during oblique loadings. The ball attachment models yielded lower von Mises stress values than the locator models at all the loading conditions, while the stress distributions were similar in the models with the same and different bone levels. Correspondingly, bone corrections due to irregularities may not be necessary in terms of biomechanics. The results of this study may provide clinicians a better understanding for the mandibular overdenture design in the cases at which different bone heights exist.